It's been couple of hours, I'm trying to install Android Marshmallow 6.0 on Raspberry Pi 3 Model B+. I tried almost every ROM but no luck so far. Can anyone guide me how to or where i can get a working version of ROM of marshmallow for Raspberry Pi 3 Model B+?

Have a look at xxxxx - it’s a straight download, write SD card and boot.

Most definitely don't purchace that! If you've purchased that, ask for a refund. RaspAnd and Arne Exton does nothing but leeches off of hard work of free and open source developers and sells it for his own personal profit (viewtopic.php?f=73&t=224852#p1381343, https://www.reddit.com/r/Android/commen ... s_9_build/). He also violates GPLv2 by failing to provide source code for the binaries he's distribtuting. If you've purchased RaspAnd, contact Arne Exton and ask him release to source code he's legally obligated to privide under GPLv2 (e.g. Linux kernel).

As for the original question, you won't find Marshmallow for 3B+ (why would you want that anyway?) but you can find newer Android versions even on this forum...